1. Field of the Invention
This invention relates to pipeline plugging devices, and in particular to a pipeline plugging apparatus that is self-energized by pipeline differential pressure across the plugging apparatus in which the radial sealing and locking pressures exerted against the pipeline are controlled to a predetermined value.
2. Description of the Prior Art
There have been a number of prior art plugging devices developed for positioning in a pipeline, either by being pigged, cable towed or motor driven, for plugging the pipeline in the event of detection of buckling or breaks in the pipeline, or to provide a downstream fluid-free environment for work or repair of the pipeline. The prior art devices that gauge the pipe for buckle detection or for detecting water due to leaks have used slips to wedge into locking engagement with the inner surface of the pipeline wall and a variety of sealing means to seal the pipeline.
However, all of these devices have operated at low pressures that have not exceeded the hydrostatic head of the seawater at the pipeline plugging depth. The prior art devices have generally not been selfenergizing to a controlled extent in response to differential pressures in the pipeline across the set plugging device due to the working fluid pressure in the pipeline. In addition, such prior art devices have not disclosed means for exerting predetermined locking and sealing pressures against the inner pipeline wall in response to a known pipeline fluid pressure in order to prevent overstressing the pipe beyond its designed yield strength.
The following U.S. Pat. Nos. are representative of the known prior patented art: 3,978,678 (Duncan, et al); 3,943,982 (Lecordier); 3,746,026 (Herring); 3,690,348 (Patterson); 3,593,749 (Reardon); and 3,525,226 (McCarron).